I like chapter breaks so I can put a bookmark in and go to bed when I need to.

Chapters vary in length between authors and within books, often, though they're usually fairly close.

I haven't really thought about this topic before. I think of a chapter as a group of related events or scenes, usually 3. My scenes are 1500-ish words long. I don't cliffhanger them, and I don't think that's strictly necessary -- we're not writing serials for newspapers! It should leave the reader wanting to turn the page, so it shouldn't be dull, either.